The balance systems for take-out sash that can be tilted and removed from between take-out jamb liners have used shoes that ride in vertical channels within the jamb liners and lock in place when the sash is tilted inward. The shoes are biased upward by counterbalance springs, and locking the shoes in place when the sash tilts inward prevents the shoes from snapping upward, under the force of the counterbalance springs, when the sash is taken out. Tilt shoes, and the locking of tilt shoes in place in take-out jamb liners, have long been troublesome, though.
One way of locking tilt shoes in place is by a cam that enlarges a dimension of the shoe when the sash tilts so that the enlarged shoe locks within the channel in which the shoe rides. Examples of this include U.S. Pat. Nos. 3,789,549; 3,797,168; 3,844,066; 4,079,549; 4,227,345; 4,364,199; and 4,590,708. Such gripper mechanisms have proved unreliable against the slippery resin surfaces of the jamb liners. Cams in tilt shoes have also operated biter knives for biting into the jamb liner to lock the shoe against the spring force. Examples of this include U.S. Pat. Nos. 3,233,278; 3,524,282; 3,611,636; 4,271,631; 4,452,012; and 4,610,108. Such biter devices have marred the jamb liner surfaces so that movement of the shoes becomes bumpy and noisy.
We have devised an improved shoe for take-out sash running between take-out jamb liners. Our shoe locks in place with a biter knife, but the knife bites into a jamb liner surface that the shoe does not ride on so that shoe movement is not roughened by biter marks. Our shoe also locks in place when the sash is removed, rather than when the sash is tilted. This is both convenient and adequate, since the shoes do not spring upward until the weight of the sash is removed from them. Our shoe includes friction pads that can be adjusted with a screwdriver to vary the friction of the shoe within the jamb liner to compensate for hop and drop. Generally, our lock shoe system is inexpensive, PG,3 reliable, durable, and easy and convenient to operate.